Means for shifting gears for changing the ratios of rotation between a drive shaft and a driven shaft are old and well known. In some constructions, the drive shaft and the driven shaft must be stopped before the gears are shifted. In other constructions, the drive shaft may be rotating and the driven shaft may be rotating or stationary when the shifting occurs. In other prior art structures, a drive shaft having freely rotatable gears mounted thereon may be temporarily connected to any one of the gears through the actuation of internal engaging means. In most constructions, the operator may select the next gear ratio he wishes to use with the mechanism passing through neutral from the previously used ratio.